RAnking functions extension methods - C# Enumerable

gistfile1.cs

public static class EnumerableExt {    
     public static IEnumerable<U> Rank<T, TKey, U>(
            this IEnumerable<T> source,
            Func<T, TKey> keySelector,
            Func<T, int, U> selector)
        {
            if (!source.Any())
            {
                yield break;
            }

            T[] ordered = source.OrderBy(keySelector).ToArray();
            TKey previous = keySelector(ordered[0]);
            int rank = 1;
            foreach (T t in ordered)
            {
                TKey current = keySelector(t);
                if (!current.Equals(previous))
                {
                    rank++;
                }
                yield return selector(t, rank);
                previous = current;
            }
        }

        public static IEnumerable<U> DescendingRank<T, TKey, U>(
            this IEnumerable<T> source,
            Func<T, TKey> keySelector,
            Func<T, int, U> selector)
        {
            if (!source.Any())
            {
                yield break;
            }

            T[] ordered = source.OrderByDescending(keySelector).ToArray();
            TKey previous = keySelector(ordered[0]);
            int rank = 1;
            foreach (T t in ordered)
            {
                TKey current = keySelector(t);
                if (!current.Equals(previous))
                {
                    rank++;
                }
                yield return selector(t, rank);
                previous = current;
            }
        }
}